diff --git a/scripts/gentests.js b/scripts/gentests.js
index 0e730d6cf..407bd1f85 100644
--- a/scripts/gentests.js
+++ b/scripts/gentests.js
@@ -5,50 +5,54 @@ var fs   = require("fs"),
     pbts = require("../cli/pbts");
 
 [
-    "tests/data/package.proto",
-    "tests/data/rpc.proto",
-    "tests/data/mapbox/vector_tile.proto",
-    "tests/data/test.proto",
-    "tests/data/convert.proto",
-    "tests/data/comments.proto"
+    { file: "tests/data/comments.proto", flags: [] },
+    { file: "tests/data/convert.proto", flags: [] },
+    { file: "tests/data/mapbox/vector_tile.proto", flags: [] },
+    { file: "tests/data/package.proto", flags: [] },
+    { file: "tests/data/rpc.proto", flags: [ "es6" ] },
+    { file: "tests/data/rpc.proto", flags: [] },
+    { file: "tests/data/test.proto", flags: [] },
 ]
-.forEach(function(file) {
-    var out = file.replace(/\.proto$/, ".js");
+.forEach(function({ file, flags }) {
+    var basename = file.replace(/\.proto$/, "");
+    var out = [ basename ].concat(flags).join("-") + ".js";
     pbjs.main([
         "--target", "static-module",
         "--wrap", "commonjs",
-        "--root", "test_" + path.basename(out, ".js"),
-        "--out", out,
+        "--root", "test_" + path.basename(basename, ".js"),
         file
-    ], function(err) {
+    ].concat(flags.map(function(flag) {
+        return "--" + flag;
+    })), function(err, output) {
         if (err)
             throw err;
         var pathToProtobufjs = path.relative(path.dirname(out), "minimal").replace(/\\/g, "/");
-        fs.writeFileSync(out, fs.readFileSync(out).toString("utf8").replace(/"protobufjs\/minimal"/g, JSON.stringify(pathToProtobufjs)), "utf8");
+        fs.writeFileSync(out, output.replace(/"protobufjs\/minimal"/g, JSON.stringify(pathToProtobufjs)));
         process.stdout.write("pbjs: " + file + " -> " + out + "\n");
         try {
             require(path.join(__dirname, "..", out));
-        } catch (err2) {
-            process.stderr.write("ERROR: " + err2.message + "\n");
+        } catch (err) {
+            if (!flags.includes("es6")) {
+                process.stderr.write("ERROR: " + err.message + "\n");
+            }
         }
     });
 });
 
 [
+    "tests/data/rpc.js",
     "tests/data/test.js",
-    "tests/data/rpc.js"
 ]
 .forEach(function(file) {
     var out = file.replace(/\.js$/, ".d.ts");
     pbts.main([
-        "--out", out,
         "--no-comments",
         file
-    ], function(err) {
+    ], function(err, output) {
         if (err)
             throw err;
         var pathToProtobufjs = path.relative(path.dirname(out), "").replace(/\\/g, "/");
-        fs.writeFileSync(out, fs.readFileSync(out).toString("utf8").replace(/"protobufjs"/g, JSON.stringify(pathToProtobufjs)), "utf8");
+        fs.writeFileSync(out, output.replace(/"protobufjs"/g, JSON.stringify(pathToProtobufjs)));
         process.stdout.write("pbts: " + file + " -> " + out + "\n");
     });
 });
\ No newline at end of file